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Flexible Cu2ZnSn(S,Se)4 (CZTSSe) solar cells have attracted considerable attention due to their potential application in specific areas such as power sources for wearable electronics. However, the over‐thick Mo(Sx,Se1−x)2 at the back contact is one of the factors that limit the device performance. Herein, a facile strategy to inhibit the thick Mo(Sx,Se1−x)2 layer by adding a proper proportion of sulfur during selenization is reported. It is found that the thickness of Mo(Sx,Se1−x)2 can be effectively tailored via tuning the proportion of S, enabling a substantial decrease in series resistance. The suppression mechanism is mainly ascribed to the change of orientation of Mo(Sx,Se1−x)2 induced by S, which limits the diffusion of Se to Mo. Accordingly, the total area efficiency of the flexible CZTSSe device improves significantly from 5.5 to 8.9% with the addition of 2% S, followed by a drop with more S. Furthermore, it is demonstrated that this strategy can also be applied to both kesterite and chalcogenide absorbers deposited on rigid Mo substrates to suppress the thick Mo(Sx,Se1−x)2 layer, indicating the universality of this method. Overall, this work provides a general, facile, and effective approach to modify the back contact interface without introducing extra blocking layers. [ABSTRACT FROM AUTHOR]

All‐inorganic perovskite of CsPbBr3 thin‐films solar cells has attracted increasing interest in recent years due to its potential long‐term stability over the generally used hybrid perovskites. Herein, all‐inorganic CsPbBr3 perovskites are doped with Eu2+ to enhance the efficiency of perovskite solar cells (PVSCs). The perovskite films exhibit a better crystallinity with smooth morphology after the introduction of rare‐earth elements. Hence, the hole‐transport layer‐free device with presence of Eu2+ and low‐cost carbon electrode achieves both enhanced efficiency and stability. In particular, the power conversion efficiency (PCE) enhances from 5.66% to 7.28% with high VOC of 1.45 V by optimizing the doping concentration of Eu2+. In addition, the storage stability measurements reveal excellent performances of PCE without encapsulation in air with relative humidity of 70–80%. These results can pave changes in future inorganic PVSCs. [ABSTRACT FROM AUTHOR]